Method and apparatus for allocating a pilot signal adapted to the channel characteristics

ABSTRACT

A set of different pilot structures are designed for use in different environments and/or different user behaviours that are expected to occur in a cell. The radio conditions for a user are estimated. Each user is then assigned an area ( 108 A-E) in resource space for its communication, which has a suitable pilot configuration. In one embodiment, the entire resource space is provided with different pilot structures in different parts ( 110 A-D) In advance and allocation of resources to the users are then performed in order to match estimated radio conditions to the provided pilot structure. In another embodiment, allocation is performed first, and then the actual pilot structure is adapted within the allocated resource space area to suit the environmental conditions.

TECHNICAL FIELD

The present invention relates generally to wireless multi-carriercommunications systems and in particular to resource allocation andpilot signals of such systems.

BACKGROUND

In most wireless systems, e.g. GSM (Global System for Mobilecommunications), WCDMA (Wideband Code Division Multiple Access), WLAN(Wireless Local Area Network), special well known training sequences orpilot signals are transmitted so that the receiver can estimate thechannel parameters sufficiently well for detection of any data signal,not previously known by the receiver. Several methods exist to do this,some use user specific pilots and some use common pilots orcombinations. Some pilots are code spread and overlaid with user data,others have dedicated time-frequency slots when pilots are transmitted.In any case, some part of the available radio resources must beallocated for pilots resulting in overhead that cannot be used for data.

In single-carrier systems, such as e.g. described in U.S. Pat. No.6,452,936, pilot data can be provided in certain time slots within atransmission frame. A shorter time interval between successive pilotdata gives a more accurate channel estimation, but decreases instead thetransmission rate. In U.S. Pat. No. 6,452,936, a particular code of theCDMA system is allocated to a user. A pilot density of a frame structureis continuously selected dependent on channel estimation information.

A multi-carrier approach has been proposed in wireless communicationssystems, in which a data stream typically is separated into a series ofparallel data streams, each of which is modulated and simultaneouslytransmitted with a different frequency. An example of a multi-carriersystem is an OFDM (Orthogonal Frequency Division Multiplexing) system.This allows a relative size of transmitted symbols relative to amultipath delay to be much larger which reduces intersymbolinterference. Such a cellular multi-user, multi-carrier wirelesscommunications system thus allows a particular user to utilise more thanone carrier simultaneously. The allocation of one or several carriersdepends typically on quality of service consideration, such as requestedtransmission rate. Generally, in a multi-carrier, multi-user system, theresource space is used in a flexible manner to give each user the bestpossible quality at each time. The principles and requirements forproviding channel estimations become in this way more complex than in asingle-carrier system, since a continuously use of a singlecommunication resource is not ensured. In a cellular multi-user,multi-carrier wireless communications system, the base station mustaccommodate many users that each experiences different channelcharacteristics due to fading in both time and frequency. Furthermore,different users travel at different speeds and thus experience differentDoppler shifts.

Today, there are a few multi-carrier systems in use. However, they arenot particularly designed for the difficult, ever changing,hard-to-predict multi-user environments that are envisioned for futurewireless systems.

For example, the systems for DVB/DAB (Digital Video Broadcasting/DigitalAudio Broadcasting) are broadcast systems that cannot take into accountthe need for individual users. Such systems must design their pilotstructure according to the worst-case scenario so that detection becomespossible even under the worst possible conditions. Such a pilotstructure gives rise to a substantial pilot overhead, and is indeednecessary in these worst-case scenarios. However, whenever the situationis better than the worst case, which typically is the case most of thetime, the pilot structure is unnecessarily extensive, giving anunnecessary pilot overhead for most users. The pilot overhead can indeedbe substantial. This reduces data capacity in the own cell andfurthermore increases the interference to the neighbouring cells (socalled ‘pilot pollution’).

Another example of a multi-carrier system is WLAN (i.e. IEEE 802.11a,IEEE 802.11g). Such a system is designed for a limited geographical areain which the users are stationary or slowly moving. The design is notintended for conditions in which the user is moving quickly or forhandling mobility in a multi-cellular environment.

In the published US patent application 2003/0215021, a communicationssystem is disclosed, in which channel characteristics are determined byanalysing a signal received over a (sub)-carrier. The determinedcharacteristics are then used to divide the sub-carriers into groups ofsimilar fading characteristics. Each group is then allocated a pilotsub-carrier. The determined pilot allocation scheme is then used forfuture transmissions across the sub-carrier. This system compensates fordifferences in fading characteristics over the carrier bandwidth, buthas a disadvantage in that it is assumed that a sub-carrier iscontinuously used for one single user. A user has to have access to alarge number of sub-carriers in order to make such a pilot allocationefficient. Furthermore, entire sub-carriers are allocated as pilotsub-carriers, which occupies a large part of the available resourcespace, contributing to the pilot pollution.

SUMMARY

The main problems with existing solutions are that pilot structures areeither not at all suitable for considerably changing radio conditions orthat they are designed for worst cases which in turn results in vastpilot overhead and “pilot pollution”.

An objective of the present invention is to provide methods and devicesfor multi-user multi-carrier wireless communications system, which arecapable to provide all users with sufficient pilots without causingunnecessary pilot overhead and pilot pollution. A further objective ofthe present invention is to provide such methods and devices, which areeasy to implement within present and planned wireless systems.

The above objectives are achieved by methods and devices according tothe enclosed patent claims. In general words, a set of different pilotstructures are designed for use in different environments and/ordifferent general radio characteristics that are expected to occur inthe cell. The radio conditions for a user are estimated, either fromdirect measurements or from knowledge about the cell characteristics,possibly combined with position information. Each user is then assignedan area in resource space for its communication, which has a suitablepilot configuration. In one embodiment, the entire resource space isprovided with different pilot structures in different parts in advanceand allocation of resources to the users are then performed in order tomatch estimated radio conditions to the provided pilot structure. Inanother embodiment, allocation is performed first, and then the actualpilot structure is adapted within the allocated resource space area tosuit the environmental conditions. For best performance, depending onsuch things as frequency selectivity, time selectivity (e.g. timedispersion and Doppler shift), and path loss the amount of pilot energyshould be adapted and the ‘distance’ between pilots in thetime-frequency domain needs to be changed.

The radio resource space can have different dimensions. In multi-carriersystems, frequency is one dimension. Other dimensions that could beutilised within the present invention are time, code, antenna and/orspatial dimensions. One or several of these dimensions span the radioresource space, in which the present invention is applied.

By adapting the pilot structure to the environment or set ofenvironments likely to occur in the cell and allocating these pilots tothe users most likely to benefit from them, an overall efficiency isachieved. The amount of pilot overhead is then connected to the actualenvironments being accommodated. Difficult environments require moreoverhead than simpler ones and hence pilot pollution is reduced on theaverage.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further objects and advantages thereof, maybest be understood by making reference to the following descriptiontaken together with the accompanying drawings, in which:

FIG. 1 is a schematic illustration of a multi-user wirelesscommunication system;

FIGS. 2A and 2B are illustrations of pilot structures in time-frequencyspace, and the allocation of different users to subspaces;

FIG. 3A illustrates a radio resource space having a code dimension;

FIG. 3B is an illustration of a pilot structure in the frequency-codesub-space;

FIG. 4 is a flow diagram illustrating an embodiment of a methodaccording to the present invention;

FIGS. 5A, 5B and 6 are diagrams illustrating pilot structures intime-frequency space, and the allocation of different users to subspacesaccording to embodiments of the present invention;

FIGS. 7A and 7B are flow diagrams illustrating other embodiments of amethod according to the present invention;

FIG. 8 is a flow diagram illustrating a part of a further embodiment ofa method according to the present invention;

FIGS. 9A to 9C are block diagrams of downlink radio management devicesof network nodes according to embodiments of the present invention;

FIG. 10 is a block diagram of uplink radio management devices of networknodes according to embodiments of the present invention;

FIG. 11 is a diagram illustrating pilot structures in time-frequencyspace having different intensities, and the allocation of differentusers to subspaces according to an embodiment of the present invention;and

FIGS. 12 and 13 are diagrams illustrating limited data descriptions ofregular pilot structure.

DETAILED DESCRIPTION

In the following description, OFDM (Orthogonal Frequency DivisionMultiplexing) systems are used for exemplifying the present invention.However, the present invention can also be applied to othermulti-carrier wireless communications systems.

In the present disclosure, “pilots” refer to signals known by a receiverand therefore used for estimation purposes. “Data” refers to signals notpreviously known by the receiver, typically user data, control signalsor broadcast information.

FIG. 1 illustrates a multi-user multi-carrier wireless communicationssystem 10, in this particular embodiment intended to be an OFDM system.Non-exclusive examples of other communications systems, in which thepresent invention is advantageously applicable, are IFDMA (InterleavedFrequency Division Multiple Access) systems, non-orthogonal orbi-orthogonal multi-carrier systems. A base station or access point 20communicates with two mobile stations or user equipments 30A, 30B. Thereis a downlink connection 22A between the access point 20 and the userequipment 30A and an uplink connection 24A between the same nodes.Likewise, there is a downlink connection 22B between the access point 20and the user equipment 30B and an uplink connection 24B between the samenodes. User equipment 30A is located at a relatively large distance fromthe access point 20, but the speed 32A (illustrated as an arrow) of theuser equipment 30A is small. User equipment 30 b is located closer tothe access point 20, but has a high speed 32B (also illustrated as anarrow). The user equipment 30A may have a relatively high need forrepetitive pilots in the frequency dimension, since the propagationconditions for the different carriers may differ considerably over thebandwidth in case of multi-path propagation with large delay spread.However, the radio conditions are probably quite slowly varying withtime due to the small speed of user equipment 30A. The user equipment30B is close to the access point, and a pilot on one frequency canprobably be used for channel estimations for many neighbouring carriers.However, the radio conditions are probably changing rapidly in time,whereby frequent pilots in time dimension are required.

FIG. 2A is a diagram of a time-frequency space. This can represent alimited portion of the entire available radio resource space 100 inthese two dimensions. Data is transmitted in quantities limited in timeand frequency. These data quantities correspond to the small squares 104in the diagram. Selected ones 102 of these data quantities contain pilotdata and are illustrated in the diagram with hatching. The pilotstructure is in this embodiment dispersed over the time-frequency spacerelatively uniformly. With this distribution, one data quantity out of11 is occupied by pilot data. The useful data transmission rate isthereby reduced by 1/11. The users of the user equipments 30A and 30B(FIG. 1) have allocated radio resources within the available radioresource space 100. User equipment 30A is allocated the resourcesub-space indicated by 108A, while user equipment 30B is allocated theresource sub-space indicated by 108B. Both users are experiencing thesame pilot density and the uniform distribution between the frequencyand time dimensions.

User 30B moves fast. The time between two consecutive pilot messages intime dimension is 11 time slots, and even if information fromneighbouring frequencies are used for channel estimation in themeantime, at least 4 time slots will pass between two consecutiveupdates. The speed of user 30B is so high that this pilot structure isnot sufficient for an acceptable quality of service.

However, arranging the pilot structure as in FIG. 2B will change thesituation. Here, there is a new update in time dimension every secondtime slot, which will supports the fast moving user equipment. Despitethis increased density in time direction, the total amount of pilot dataquantities is reduced somewhat. Now only one data quantity out of 12comprises a pilot. The overhead has decreased from 1/11 to 1/12 (about9%).

However, user equipment 30A now achieves problems. This user equipment30A moves slowly and is of limited use of the frequent updating in time.However, it has need for more closely located pilots in frequencydimension instead. The pilot structure of FIG. 2B becomes veryunsuitable for user equipment 30A.

So far, only two dimensions, time and frequency, have been discussed.FIG. 3A illustrates a radio resource space in three dimensions, time,frequency and code. In such a system, each data quantity will insteadcorrespond to a small cube 104. Generalisation can be performed tohigher order spaces, comprising e.g. antenna or space dimensions. Ingeneral, any radio resource space in at least two dimensions, of whichone is frequency, can be used with the present invention.

FIG. 3B illustrates a pilot pattern in a frequency-code space for aspecified time. In this example 16 different codes are available andalso 16 different frequencies. The illustrated pilot pattern leads tothat the pilots are transmitted on all frequencies during the specifiedtime duration, however, spread out in the code dimension. One code ineach frequency is occupied by a pilot, whereas the remaining 15 codesare used for data transmission.

As mentioned briefly above, more generally the antenna or spatialdimensions could also be part of the resource space. One example is thatdifferent frequency bands are allocated to different beams of amulti-sector or fixed beam site. In this case, the spatial dimension ispart of the description since different pilot patterns may be deployedfor the different beams that overlap in the spatial domain. With thegrouping of resources in terms of antenna sectors or beams the pilotsallocated to different users can change dynamically when the user forexample moves between sectors and the sectors have different frequencybands allocated to them. In such cases, antenna or spatial dimension canalso be used as additional dimensions in a total resource space.

The flow diagram of FIG. 4 illustrates the main steps of an embodimentof a method according to the present invention. The procedure starts instep 200. In step 202, a number of pilot configurations are provided,which are believed to suit different radio conditions appearing in thecell in question. At least two such pilot configurations are available,i.e. they can be handled by both sides of the transmission connection.At least one of the pilot configurations comprises sub-carriers havingboth pilot resources and data resources, i.e. resources allocated forany data not previously known by the receiver, such as user data,control signals or broadcast information, in order to accommodateefficiency requests from e.g. slow-moving terminals. The transmittermanages the sending of pilots according to this configurations and thereceiver is capable of performing channel estimation based on the atleast two pilot configurations. In step 204, an estimation of the radioconditions at the receiver is obtained. This estimation can be providedin many different ways. The actual radio conditions can be measured andevaluated. Another possibility is to assume an estimate from knowledgeabout the characteristics in the cell and possibly based on e.g.location and/or speed of the receiver relative the transmitter.

In step 206, a user is allocated resources in resource space, which havea pilot configuration that is matched to the estimated radio conditions.This matching can be performed in different manners, described more indetail further below. The procedure stops in step 299. Anyone skilled inthe art realises that step 202 preferably is performed once, and theprovided pilot structures can then be used for any future allocation ofusers, or re-allocation of existing users.

A few examples, using OFDM as an example system, will be used tovisualise the effect of the present invention. The basic setup in FIG.5A is assumed as follows. During a certain time period and seen over allfrequency resources, the available radio resources constitute a grid ofbasic resources that can be used for data, control signaling or pilotsignals or other signals as discussed earlier. The resolution infrequency dimension is one OFDM carrier and in time it is one OFDMsymbol. Pilot symbols are as above depicted with hatched boxes.

The transmitter side, in this example assumed to be the base station,determines a number of different pilot patterns and assigns these pilotpatterns to different parts of the entire radio resource space. Thepilot patterns may for example be periodically recurring with someperiod or pseudo-randomly designed. This means that different parts ofthe radio resource space have a denser or at least differing pilotpattern than other parts. Each pilot pattern is intended to accommodateusers experiencing different channel characteristics.

This is illustrated in FIG. 5A. The entire radio resource spaceillustrated is divided into four rectangular parts, 110A-D. The resourcespace part 110A has a pilot pattern, having a dense occurrence in timedimension (every second OFDM symbol at certain carriers), but a moredispersed behaviour in the frequency dimension (only every sixth OFDMcarrier). The resource space part 110B has a very diluted pilot pattern,having only one pilot in 36 resource units, evenly spread in time andfrequency dimensions. The resource space part 110C is the opposite ofpart 110A, with a dense pilot pattern in frequency dimension, but sparsein time dimension. Finally, resource space part 110D has a very densepilot structure in both dimensions, comprising a pilot symbol in everyfourth resource unit.

According to one embodiment of the invention, the users are nowallocated to the different parts of the radio resource space dependenton their estimated radio conditions. In other words, whenever a certainuser has certain demands, the user is assigned resources in the resourcespace where pilots with the appropriate density can be utilised forchannel estimation. In the situation in FIG. 5A, there are pilotstructures suitable for typically four combinations of Doppler and delayspread. In part 110A, the pilot structure is intended for a largeDoppler and low delay spread. In part 110B, the pilot structure isintended for a low Doppler and low delay spread. In part 110C, the pilotstructure is intended for a low Doppler and high delay spread. In part110D, the pilot structure is intended for a high Doppler and high delayspread.

A first user, having radio conditions demanding a high density of pilotsin both dimensions is allocated to the resource sub-space 108A withinthe part 110D. A second user, only having need for dense pilot in thetime dimension is allocated resources in a resource sub-space 108Bwithin the part 110A. A third user with very favourable radio conditionsis allocated to a resource sub-space 108C in part 110B. Finally, twomore users, having high demands on pilot density are given resources intwo sub-spaces 108D and 108E, respectively in part 110D. One realisesthat each user has achieved a pilot pattern that is suited to itsindividual needs. It is beneficial, e.g. to assign resources for mobileswith certain fast varying channel or Doppler conditions in the denseparts of the pilot pattern and users with more slowly varying conditionsin the less dense parts.

Note that the base station does not need to transmit all pilots at alltimes. Only pilots that in fact can be utilised by any user needs to betransmitted. If a pilot resource at time of transmission cannot beutilised by any data symbol that some user need to detect with the helpof said pilot, then the pilot need not be transmitted. In such a way,the overall pilot pollution is reduced, and so is the averagetransmission power.

In FIG. 5B, a further embodiment of the present invention is mustrated.Assume the same situation as was present in FIG. 5A. Three users areoccupying all resources in the densest part 110D. E yet another userwith need for a very dense pilot configuration appears, the pre-definedpilot configuration plan of FIG. 5A becomes insufficient. However, thenew user can be allocated to a free resource sub-space 108F, preferablyin connection with the part 110D. This sub-space 108F had originally apilot pattern according to part 110C, but when allocating the user, thepilot pattern is adjusted to match the demands put by the new user. Insuch a way, the original pre-determined division into different parts inthe resource space can be adapted to the actual need. However, if a goodinitial configuration is used, most cases are covered and the frequencyof adjustments is low.

Now, return to the situation of FIG. 5A. If the user having theallocation of sub-space 108E slows down, the estimated radio conditionschange, and the need for pilots is reduced. The user can then bereallocated to another sub-space of the resource space, having a moresuitable pilot configuration for the new estimated radio conditions,e.g. to part 110C. An alternative is to keep the allocated sub-space butinstead change the pilot pattern to a more suitable one for the newconditions.

The ideas of adjusting or adapting the pilot configuration when neededcan also be brought to the extreme end, where no pilot pattern at all ispre-configured for the different parts of the resource space. Instead,there is always an adjustment of pilot pattern for all users. This isschematically illustrated in FIG. 6. Here, a first user was assigned asub-space 108A, without associated pre-defined pilot pattern. The pilotpattern was then adjusted according to the actual needs as concludedfrom the estimated radio conditions. In this case a dense pattern wasselected. A second user was allocated to sub-space 108B andsubsequently, a suitable pilot pattern was selected for his sub-space.In such a way, all the sub-spaces 108A-F were associated with pilotconfigurations suitable for each individual need. Sub-spaces notallocated to any user do not comprise any pilots in such an approach. Auser with certain estimated properties is thus allocated to use certainresources and the pilot pattern is designed accordingly. The result isthe same as the previous embodiments, pilot patterns and usercharacteristics are matched.

The above embodiments can also be expressed in flow diagrams. In FIG.7A, a flow diagram corresponding to the situation in FIG. 5A isillustrated. The resource space is in step 203 provided with at leasttwo different pre-determined pilot configurations at different parts ofthe resource space. Step 204 is unchanged compared to FIG. 4. In step207, the matching of the radio conditions and pilot structures isperformed by selecting a suitable resource space.

The situation in FIG. 5B is illustrated by the flow diagram of FIG. 7B.Also here, pre-defined pilot configurations are associated withdifferent parts of the resource space in step 203. In step 205, it isdetermined whether there is any available resources in parts that aresuitable for the particular estimated radio conditions for the user tobe allocated. If there are resources with suitable pilot structuresavailable, the procedure continues to step 207, as in FIG. 7A. If noresource space with appropriate pilot structure is available, any freeresource space is allocated in step 209, however, preferably in thevicinity of the part having a suitable pilot pattern. In step 210, thepilot configuration is adapted within the selected resource sub-space tomatch the estimated radio conditions.

The embodiment illustrated in FIG. 6 can similarly be illustrated by thepart flow diagram of FIG. 8. Here, the step 206 in FIG. 4 is describedin more detail. In step 208, an area is selected as a resource sub-spacefor the user. In step 210, the pilot configuration in the selected areais adapted to the need connected to the estimated radio conditions ofthe user. Note the similarities between FIG. 7B and FIG. 8.

The present invention can be implemented for wireless communicationbetween any nodes in a communications system. Such nodes can be e.g.user equipment, mobile station, base station, access point or relay. Inthe examples below, the most straightforward situation withcommunication between a base station and a user equipment will bediscussed as an example. The scope of the claims should, however, not beaffected by this example.

Multi-carrier communication is typically most applied in downlinkconnections. In FIG. 9A, a wireless communications system according toan embodiment of the present invention is illustrated. A base station 20communicates with a mobile terminal 30 via an uplink 24 and a downlink22 connection. In the downlink communication, the ideas of the presentinvention are implemented. The base station 20 comprises a downlinkcontrol unit 25, which is enlarged in the lower part of FIG. 9A. Thedownlink control unit 25 is responsible for allocating resources forcommunication on the downlink 22 between the base station 20 and themobile terminal 30 and comprises in turn a pilot manager 26 and a radiocondition processor 28. Similarly, the mobile terminal or user equipment30 also comprises a downlink control unit 35, also enlarged in the lowerpart of FIG. 9A. The downlink control unit 35 comprises a channelestimator 36 and a measurement unit 38 for radio conditions.

The radio conditions measurement unit 38 measures the actual radioconditions at the user equipment 30. Such measurements can comprise e.g.Doppler shift and signal strength as well as power delay profile,channel impulse response, time and frequency selectivity measurementsand interference levels. The results of the measurements are transferredto the radio conditions processor 28 of the base station 20, preferablyby the uplink communication link 24. The radio conditions processor 28evaluates the measured conditions and translates it to estimated radioconditions for the user equipment 30. In other words, the radioconditions processor 28 obtains data associated with estimated radioconditions for the user equipment 30. In a basic version, the estimatedradio conditions could e.g. comprise two flags, one indicating low orhigh Doppler shift and one indicating small or large delay spread. Whenhaving a radio resource space in frequency and time dimensions,quantities associated with coherence bandwidth and coherence time,respectively, are of interest. The estimated radio conditions areforwarded to the pilot manager 26, which performs the actual selectionand/or adjustment of resource sub-spaces. The pilot manager 26 thusprovides access to the use of the different pilot configurations. Whenpre-defined pilot patterns are used, the pilot manager selects in whichpart of the multi-carrier space the allocated resource sub-space will beplaced. Without pre-defined patterns in different parts of themulti-carrier space, the pilot manager 26 comprises functionalities forselecting a multi-carrier sub-space for allocation and functionalitiesto adapt the pilot pattern of that selected sub-space according to theestimated radio conditions. When the pilot manager has decided whatpilot pattern to apply, the user equipment 30 has to be informed aboutthe selection, in order to be able to perform the right channelestimation upon reception of the data. The pilot manager 26 thuscomprises means for transferring suitable data to the channel estimator36.

In FIG. 9B, another embodiment is illustrated, where the base station 20has the entire responsibility for the selection of pilot structure. Thedownlink control unit 25 here also comprises a position estimator 29.The position estimator 29 provides an estimation of the position of theuser equipment 30 and preferably also the velocity. This can beperformed in any manner, e.g. according to prior art methods, and is notfurther discussed here. The position is forwarded to the radio conditionprocessor 28. The radio condition processor 28 has access to knowledgeabout the different environments within the cell. A cell could e.g.cover a first area having generally slowly moving user equipments, and asecond area, were the average speed is considerably higher. The positionestimation could reveal the location of the user equipment, i.e. if itis situated in the high- or low-speed area. From such information, theradio condition processor 28 can conclude what radio conditions thatshould be assumed for the user equipment. Such estimation then forms thebase on which the pilot pattern is selected.

In FIG. 9C, yet another embodiment is illustrated. In this embodiment,the user equipment 30 makes more efforts in the procedure to findsuitable pilot structures. The downlink control unit 35 hereadditionally comprises a radio conditions processor 39. This means thatboth the measurements and the evaluation of the measurements areperformed in the user equipment 30. The estimated radio conditions arereported to the base station 20, e.g. in the form of data representingcoherence bandwidth and coherence time, respectively. Alternatively, theradio conditions processor 39 can also select an appropriate pilotpattern and transmit a request to use such a pattern to the base station20. The base station 20 can in such a case either follow therecommendation or overrule it and make an own decision.

FIG. 10 illustrates one possible configuration for uplink communication.The base station 20 comprises an uplink control unit 45, in turncomprising a radio conditions measurement unit 21, a radio conditionsprocessor 28 and a pilot manager 26. The operations of the units aresimilar to the ones in the downlink case, but adapted for uplinkcommunication instead, i.e. it is the radio conditions of the receivedsignals from the user equipment 30 that are of importance. The pilotmanager 26 decides which pilot pattern that is appropriate to apply, andtransmits a request to an uplink control unit 55 in the user equipment30. In a basic version, the uplink control unit 55 simply applies theproposed pilot pattern on its uplink traffic. The uplink control unit 35of the base station 20 also comprises a channel estimator 27 in order tobe able to detect the data sent on the uplink. This channel estimator 27is also informed about the pilot structure to use.

FIG. 11 illustrates yet another embodiment of the present invention, inwhich one makes use of the possibilities to vary the intensity to reducepilot pollution. In parts 110A and 110D, all or some of the pilot datais marked to be transmitted with a lower (or zero) intensity. If a userequipment using the pilot signals is close to the base station, thetransmission power does not have to be equally high to obtain areasonable channel estimation compared with user equipments situatedfurther away from the base station in such a way, it is also possible tovary the pilot intensity throughout the resource space. Such intensityconfigurations can as above be performed either in advance or asadjustment procedures.

The pilot symbols can also be transmitted with different power fordifferent classes of users and depending on path loss. The power levelscan either be dynamically varying between zero and a given numberP_(max) or be defined in advance. Note that a power level equal to zerois equivalent to no pilots for this slot, enabling the use of this slotfor other purposes, such as data. If the power is dynamically varying,the power levels have to be signaled to the receiver for appropriatetreatment.

When there are several possible pilot patterns to use in a system, thereceiver has to be informed about which one is actually used if anumbered set of pre-determined pilot patterns are used, theidentification number of the pilot pattern is sufficient. However, moreelaborate systems can use different pilot patterns for different cuesand the numbering of patterns can be difficult to manage. In such acase, a solution is to transfer a complete description of the pilotpattern to be used. For regular pilot patterns, the amount of data thatis needed to uniquely define the patterns is quite limited.

In FIG. 12, a pilot pattern is illustrated within a resource sub-spacein frequency and time dimensions. The resource sub-space is reportedanyway, and is typically defined by frequency and time “coordinates” andthe number of frequency DF and time DT slots that are comprised in thesub-space. The pilot pattern is then easily characterised by only threevectors in the (two-dimensional) resource space. A first vector V0defines the “distance” in frequency and time, respectively, between awell-defined position in the sub-space, e.g. the lower left corner asillustrated in the picture, and any pilot data within the pattern. Asecond vector V1 defines a “relative distance” between the two closestpilots in the pattern. A third vector V2 defines a “relative distance”between the second closest pilots, that is not aligned with the firstvector V1. By knowing only these vectors, the entire pilot pattern caneasily be calculated.

Also somewhat more complicated patterns can be fit into a similar model.In FIG. 13, a pattern having two neighbour pilots distributed in pairsover the resource space. In order to describe this pattern, only oneextra vector is needed, the relative vector between the two pilots ineach pair. Anyone skilled in the art realises that with a very limitednumber of data, rather complex pilot patterns can easily be defined.

It will be understood by those skilled in the art that variousmodifications and changes may be made to the present invention withoutdeparture from the scope thereof, which is defined by the appendedclaims.

1-36. (canceled)
 37. Method for wireless communication in a multi-user,multi-carrier communications system, using a multi-carrier resourcespace of at least two dimensions, of which one is frequency, saidmulti-carrier communications system allowing a data stream to beseparated into a series of parallel data streams, each of which ismodulated and simultaneously transmitted with a different frequency,comprising the step of: allocating a first resource sub-space of entiresaid multi-carrier resource space for communication between a first nodeand a second node; said first resource sub-space comprising resources ofmore than one carrier; obtaining data associated with estimated radioconditions for communication between the first node and the second node;allocating a second resource sub-space of entire said multi-carrierresource space for communication between the first node and a thirdnode; said second resource sub-space comprising resources of more thanone carrier, obtaining data associated with estimated radio conditionsfor communication between the first node and the third node; andproviding access to the use of at least two pilot resourceconfigurations, intended for different estimated node radio conditions,whereby the first resource sub-space is associated a pilot resourceconfiguration, being in agreement with pilot need for the estimatedradio conditions for the second node and the second resource sub-spaceis associated a pilot resource configuration, being in agreement withpilot need for the estimated radio conditions for the third node; andwhereby at least one of the first resource sub-space and the secondresource sub-space comprises a carrier having both pilot resources anddata resources within said first resource sub-space or said secondresource subspace, respectively.
 38. Method according to claim 37,wherein the entire multi-carrier resource space being divided into partshaving different pilot resource configurations; whereby the steps ofallocating comprises the steps of selecting the first resource sub-spaceand the second resource sub-space in respective parts having a pilotresource configuration suitable for the estimated radio conditions forthe second node and the third node, respectively.
 39. Method accordingto claim 38, comprising the further steps of: selecting, if no resourcespace part having a pilot resource configuration suitable for theestimated radio conditions for the second node or the third node,respectively, is available, an arbitrary first multi-carrier resourcesub-space; and adapting the pilot resource configuration within thefirst multi-carrier resource sub-space to suit the estimated radioconditions for the second node or the third node, respectively. 40.Method according to claim 37, further comprising the steps of: selectingthe first multi-carrier resource sub-space; selecting the secondmulti-carrier resource sub-space; and adapting the pilot resourceconfiguration within the first and second multi-carrier resourcesub-space to suit the estimated radio conditions for the second node andthe third node, respectively, after the step of selecting.
 41. Methodaccording to claim 37, wherein the multi-carrier resource space has atime dimension.
 42. Method according to claim 37, wherein themulti-carrier resource space has a code dimension.
 43. Method accordingto claim 37, wherein the multi-carrier resource space has a spatialdimension.
 44. Method according to claim 37, wherein the steps ofobtaining in turn comprises the steps of estimating a set of estimatedradio conditions.
 45. Method according to claim 44, wherein the set ofestimated radio conditions comprises at least one of Doppler conditionsand coherence time conditions.
 46. Method according to claim 44, whereinthe set of estimated radio conditions comprises at least one of delayspread conditions and coherence bandwidth conditions.
 47. Methodaccording to claim 44, wherein the steps of estimating are based onposition and/or velocity information concerning the second node and thethird node, respectively.
 48. Method according to claim 37, wherein thesteps of obtaining comprises the steps of receiving instructions and/orsuggestions about preferred pilot resource configuration.
 49. Methodaccording to claim 37, wherein the first node is selected from the groupof: user equipment; mobile station; base station; access point; andrelay.
 50. Method according to claim 37, wherein at least one of thesecond node and the third node is selected from the group of: userequipment; mobile station; base station; access point; and relay. 51.Method according to claim 37, wherein resources of the first and secondresource sub-spaces are allocated for downlink communication.
 52. Methodaccording to claim 51, wherein the steps of obtaining data associatedwith estimated radio conditions for the second node and the third nodeis performed in a base station or access point.
 53. Method according toclaim 52, further comprising the steps of transferring datacharacterising the first pilot resource configuration from the basestation or access point to the second node and transferring datacharacterising the second pilot resource configuration from the basestation or access point to the third node.
 54. Method according to claim37, wherein resources of the first resource sub-space and the secondresource sub-space are allocated for uplink communication.
 55. Methodaccording to claim 54, wherein the steps of obtaining data associatedwith estimated radio conditions for the second node and for the thirdnode are performed in a base station or access point, followed by thesteps of transferring the data associated with estimated radioconditions for the second node to the second node and transferring thedata associated with estimated radio conditions for the third node tothe third node.
 56. Method according to claim 54, wherein the step ofobtaining data associated with estimated radio conditions for the secondnode is performed in the second node and the step of obtaining dataassociated with estimated radio conditions for the third node isperformed in the third node.
 57. Method according to claim 56, furthercomprising the steps of transferring data characterising the first pilotresource configuration from the second node to the first node andtransferring data characterising the second pilot resource configurationfrom the third node to the first node.
 58. Method according to claim 37,further comprising the step of refraining from transmitting pilots inareas of the entire multi-carrier resource space not being allocated.59. Method according to claim 37, wherein the wireless communicationutilises OFDM.
 60. Method according to claim 37, wherein the availableat least two pilot resource configurations comprises differentdistribution patterns of pilot symbols in the multi-carrier resourcespace.
 61. Method according to claim 60, wherein the available at leasttwo pilot resource configurations further comprises transmission ofpilot symbols with differing intensity.
 62. A first node of amulti-user, multi-carrier wireless communications system using amulti-carrier resource space of least two dimensions, of which one isfrequency, said first node being arranged for handling a data streamseparated into a series of parallel data streams, each of which beingmodulated and simultaneously transmitted with a different frequency, thefirst node comprising: means for allocating a first resource sub-spaceof entire said multicarrier resource space for communication between thefirst node and a second node; said first resource sub-space comprisingresources of more than one carrier; means for obtaining data associatedwith estimated radio conditions for communication between the first nodeand the second node; means for allocating a second resource sub-space ofentire said multi-carrier resource space for communication between thefirst node and a third node; said second resource sub-space comprisingresources of more than one carrier; means for obtaining data associatedwith estimated radio conditions for communication between the first nodeand the third node; and means for providing access to the use of atleast two pilot resource configurations, intended for differentestimated node radio conditions, whereby the first resource sub-spacecomprises a pilot resource configuration, being in agreement with pilotneed for the estimated radio conditions for the second node and thesecond resource sub-space comprises a pilot resource configuration,being in agreement with pilot need for the estimated radio conditionsfor the third node, and whereby at least one of the first resourcesub-space and the second resource sub-space comprises a carrier havingboth pilot resources and data resources within said first resourcesub-space or said second resource subspace, respectively.
 63. Nodeaccording to claim 62, wherein the entire multi-carrier resource spacebeing divided into parts having different pilot resource configurations;whereby the means for allocating being arranged for selecting the firstresource sub-space in a part having a pilot resource configurationsuitable for the estimated radio conditions for the second node and forselecting the second resource sub-space in a part having a pilotresource configuration suitable for the estimated radio conditions forthe third node.
 64. Node according to claim 62, further comprising:means for selecting the first multi-carrier resource sub-space; meansfor selecting the second multi-carrier resource sub-space; and means foradapting the pilot resource configuration within the first multi-carrierresource sub-space to suit the estimated radio conditions for the secondnode and for adapting the pilot resource configuration within the secondmulti-carrier resource sub-space to suit the estimated radio conditionsfor the third node, the means for adapting being connected to an outputof the means for selecting.
 65. Node according to claim 62, furthercomprising: means for transferring data characterising the first pilotresource configuration from the first node to the second node and fortransferring data characterising the second pilot resource configurationfrom the first node to the third node.
 66. Node according to claim 62,wherein the means for obtaining data associated with estimated radioconditions for the second node in turn comprise a receiver for receivinginstructions and/or suggestions about preferred pilot resourceconfiguration from the second node and the third node.
 67. Nodeaccording to claim 62, being arranged for OFDM.
 68. Node according toclaim 62, being a node selected from the group of: user equipment;mobile station; base station; access point; and relay.
 69. Nodeaccording to claim 62, wherein the second node is selected from thegroup of: user equipment; mobile station; base station; access point;and relay.
 70. Wireless communications system, being a multi-user,multi-carrier wireless communications system using a multi-carrierresource space of least two dimensions, of which one is frequency, saidwireless communications system being arranged for handling a data streamseparated into a series of parallel data streams, each of which beingmodulated and simultaneously transmitted with a different frequency,comprising at least one node, said at least one node in turn comprising:means for allocating a first resource sub-space of entire saidmulti-carrier resource space for communication between the first nodeand a second node; said first resource sub-space comprising resources ofmore than one carrier; means for obtaining data associated withestimated radio conditions for communication between the first node andthe second node; means for allocating a second resource sub-space ofentire said multi-carrier resource space for communication between thefirst node and a third node; said second resource sub-space comprisingresources of more than one carrier; means for obtaining data associatedwith estimated radio conditions for communication between the first nodeand the third node; and means for providing access to the use of atleast two pilot resource configurations, intended for differentestimated node radio conditions, whereby the first resource sub-spacecomprises a pilot resource configuration, being in agreement with pilotneed for the estimated radio conditions for the second node and thesecond resource sub-space comprises a pilot resource configuration,being in agreement with pilot need for the estimated radio conditionsfor the third node, and whereby at least one of the first resourcesub-space and the second resource sub-space comprises a carrier havingboth pilot resources and data resources within said first resourcesub-space or said second resource sub-space, respectively.
 71. Userequipment being arranged to handle connection to a multi-user,multi-carrier wireless communications system using a multi-carrierresource space of least two dimensions, of which one is frequency, saiduser equipment being further arranged for handling a data stream to beseparated into a series of parallel data streams, each of which ismodulated and simultaneously transmitted with a different frequency,comprising: means for communication between the user equipment and anode utilising a first resource sub-space of entire said multi-carrierresource space; said first resource sub-space comprising resources ofmore than one carrier; said first resource sub-space comprising a firstpilot resource configuration, out of a set of at least two differentpilot resource configurations; whereby the first pilot resourceconfiguration being in agreement with pilot need for estimated radioconditions for the user equipment; and whereby the first resourcesub-space comprises a carrier having both pilot resources and dataresources within said first resource sub-space.
 72. User equipmentaccording to claim 71, further comprising: receiver for receiving datacharacterising the first pilot resource configuration from the node;means for channel estimation, connected to the receiver, whereby themeans for channel estimation is arranged to perform channel estimationbased on the received data characterising the first pilot resourceconfiguration.